Sustainability of Water Resources and Agricultural Production in Semi-arid Regions

Human activity is the leading driver of geomorphological changes on the surface of the planet earth. One of the ways this has happened is through an unprecedented demand for water due to population growth, industrialization, urbanization and agricultural production. The current mode of agricultural activity has a significant influence on hydrological processes in especially arid and semiarid ecosystems. This has put a huge stress on water resources and the dependent ecosystems and biodiversity. With 20% of the world population and only 6% of global surface freshwater resources, China draws heavily on groundwater for its freshwater needs. In the semiarid North China Plain (NCP), agriculture accounts for some 70% of total water use. Over 80% of this water is pumped from the aquifers beneath the plain. The intensive groundwater exploitation has become a worrying concern for sustainable agricultural production that will avert water crisis in the plain region. The research task of this study was to analyze water storage dynamics and the related impacts on crustal matrix in North China Plain. The study used data products from GRACE (Gravity Recovery and Climate Experiment), GLDAS (Global Land Data Assimilation System), field-measured groundwater level and GPS (Global Positioning System) to analyze for water storage depletion and land subsidence in the region. The study showed that average water storage depletion in the region was 23.76±1.74 mm/yr, which is the equivalent of 3.26±0.24 km3/yr of the 137,000 km2 study area. This is 7.23±0.53% of the slated 45 km3/yr water delivery in the region in 2050 through the South-North Water Diversion Project. The cumulative water storage depletion for the investigated 8-year period (2002-2009) was 26.04±1.91 km3, which is 57.87±4.24% of the slated water delivery in 2050. About 79.25% (18.83±1.38 mm/yr; 2.58±0.19 km3/yr) of the water storage depletion was from groundwater storage and 20.75% (4.93±0.36 mm/yr; 0.68±0.05 km3/yr) from soil moisture storage. Analysis of GPS data of relative land surface change for 2002-2009 suggested the occurrence of land subsidence which was on the order of 7.29±0.35 mm/yr in the vertical component of IGS08 station in Beijing. The adjusted land subsidence for the entire North China Plain study area was estimated at 2.74±0.16 mm/yr. Assuming that the subsidence was all drainable water, the subsidence-driven aquifer material compaction caused an additional 0.12±0.01 km3/yr water storage loss in the 16,000 km2 Beijing zone and 0.38±0.02 km3/yr in the 137,000 km2 North China Plain study area. Also, the estimated water storage loss (0.38±0.02 km3) due to land subsidence was ~12% of the GRACE-estimated total water storage depletion (3.26±0.24 km3/yr) in the study area. After adjustment for subsidence-induced storage loss, storage depletion in the study area was estimated at 21.02±1.58 mm/yr (2.88±0.22 km3/yr) in total water storage, 16.66±1.25 mm/yr (2.28±0.17 km3/yr) in groundwater storage and 4.36±0.33 mm/yr (0.60±0.05 km3/yr) in soil moisture storage. Water storage depletion in conjunction with land subsidence could be a disastrous concurrence with adverse implications for the ecosystem, biodiversity, food security, social stability and the livelihood of millions of people in the region and beyond. Because the long-term benefits of efficient and sustainable water use far outweigh the short-term benefits of the current water exploitation mode, it is critical for all relevant stakeholders — including water users (e.g., producer farmers), water service providers (e.g., contracted companies) and water policy makers (e.g., governments) — to embark on measures that ensure efficient and sustainable water use in the study area. Identification of viable alternative water sources (like the South-North Water Diversion Project) could limit water storage depletion and its related aftereffects like subsidence in the region. Also, strategies such as managed aquifer recharge, increased water use efficiency, brackish water use, inter-basin/regional water transfers and various combinations of such strategies could enhance groundwater storage in the study area.